Parenteral liquid administration sets are utilized for administering blood, or parenteral solutions such as normal saline, normal glucose, Ringers solution, or the like, typically into the vein of a patient.
It is long been known that foreign particulate material, particularly that having a particle size of above five microns, is highly undesirable for administration. However, inevitably, small amounts of such particulate material are found in extracorporeal blood and parenteral solutions. Because of this, blood has long been passed through a filter in its administration set, immediately prior to infusion in the patient.
At the present time, there is also growing interest in the filtration of other parenteral solutions immediately prior to administration, to remove particulate material.
Blood filters must have a pore size large enough to allow blood cells to pass. However, when filters for solutions having smaller pore sizes, on the order of 5 microns or less, are used, the problem of "air-blocking" can arise. This occurs when, as the set is being primed by aqueous parenteral solution, the aqueous liquid comes into contact with the 5 micron filter before all of the air upstream of the filter has passed through it. If such a filter is hydrophilic in nature, as such filters generally must be in order to pass aqueous liquids, wetting of the filter will tend to prevent the passage of air.
Accordingly, the air accumulates in a large bubble behind the filter until it frequently stops flow of liquid through the filter. If this happens, the solution administration set is disabled until the user manages to force the air through the filter by pressure, or the set is disconnected from the parenteral solution source, and the air bubbles shaken out of the inlet of the set. This latter expedient is an undesirable and non-sterile procedure.
Frequently, in case of air-blocking, the entire set must be discarded and another set primed for use.
In the prior art, it has been suggested in Keedwell U.S. Pat. No. 3,520,416 to prepare a microporous filter for parenteral solution sets in which certain portions of a hydrophilic filter material are rendered hydrophobic by the application of a silicone material or the like, in a pattern of repeating stripes or dots, etc. However, this suggestion has the significant disadvantage that it is impractical for use with the very small filters which are desirable for use with the typical, commercial parenteral solution administration sets.
For example, it is generally unnecessary for the overall area of the filter in the set to be even as much as one square centimeter. Usually, the total filter surface area can be about 0.6 square centimeter.
In attempting to use the Keedwell solution to the problem of air-blocking, it becomes very difficult to precisely control the exact ratio of the area of silicone-treated filter membrane to the area of untreated hydrophilic membrane area in the manufacture of such a small filter. Accordingly, mass-produced solution administration sets having filters that attempt to utilize the Keedwell invention may have substantially variable performance, because of the difficulty of precisely controlling the ratio of silicone-treated areas to the untreated hydrophilic areas, when the total filter surface area is less than a square centimeter.
Also, it is not possible for the hydrophobic and hydrophilic filter filter portions, in Keedwell, to have different pore sizes or to be made from different basic materials. This reduces the flexibility of use and design of structures incorporating that invention.
It is also known in patents such as Rosenberg U.S. Pat. Nos. 3,523,408 and Riely, et al. Pat. No. 3,631,654 to provide a filter having separate pieces of hydrophobic and hydrophilic filter material. However, in these devices, the hydrophobic filter members are exposed to the exterior. Accordingly, breakage of the hydrophilic filter member can cause, in conjunction with a suction pressure head of an administration set, the suction of exterior air into the administration set downstream from the filter. If a pump is utilized for pressure administration of liquid to a patient, the results of this can be fatal, since the sucked air can be directly pumped into the patient.
By the invention of this application, a filter for an I. V. administration set is provided in which the ratio of hydrophobic filter area to hydrophilic filter area can be precisely and routinely controlled on a mass production basis. Also, the pore sizes of the respective filter materials can be individually selected to be of the exact, desired size for optimum functioning for the intended purpose. Similarly, the filter is safe in the event of rupture of the filter members for any reason, since the filter members are closed from the exterior. Accordingly, a defective filter will result in no injury, and will merely fail, to a greater or lesser extent, in its filtering function.